The present invention relates to an organic electroluminescence device (hereinafter sometimes called xe2x80x9corganic EL devicexe2x80x9d or xe2x80x9cEL devicexe2x80x9d). More particularly, the present invention relates to an organic EL device suitably used for display apparatuses for home use or industrial use, light sources for printer heads, and the like.
An example of conventional organic EL devices is disclosed in JP-A-7-78689. The organic EL device disclosed in this patent application has an objective of obtaining high luminescent brightness. This EL device is characterized in that the wavelength of an interference peak (A2) is coincided with the wavelength of a intensity peak (B2) of light produced in an organic light-emitting layer as shown in FIG. 20. Specifically, an interference effect occurs when light produced in an organic light-emitting layer passes through several thin film layers. The objective of the invention of the above-described patent application is to accord the wavelength of the interference peak due to this interference effect with the wavelength of the intensity peak for light produced in the light-emitting layer.
However, if the interference peak wavelength due to the interference effect is coincided with the intensity peak wavelength, a tendency for a color purity (CIE chromaticity coordinates) decrease is experienced. For example, a blue light of organic EL device with a intensity peak wavelength in the range of 400 to 490 nm includes green light components with a high luminous efficacy. If the interference peak wavelength is coincided with the intensity peak wavelength, the intensity of the green light components is also increased, resulting in a tendency for a decrease in the color purity (CIE chromaticity coordinates).
Also, JP-A-7-240277 discloses an organic EL device in which the total optical thickness of high refractive index transparent electrodes and organic light-emitting layers is designed so as to increase the center wavelength value.
However, in this organic EL device, a color purity decreases because an increase in the center wavelength value also entails an increase in the intensity at neighborhood of the center wavelength.
A constant CIE color coordinate value can be obtained if the thickness of the organic light-emitting layers is definitely uniform and does not fluctuate any more. However, this is not practical because such an organic light-emitting layer can be produced only at the extreme sacrifice of production yield.
As a result of extensive studies to solve these problems, the inventors of the present invention have found the following things, namely, the CIE chromaticity coordinate values which is measured in accordance with JIS Z 8701, periodically varies with peaks and valleys corresponding to the total optical path length of a transparent electrode and an organic layer. Thus, a change in the CIE chromaticity coordinate value can be decreased if the thickness of the organic layer is determined taking the values for such peaks and valleys into consideration so that the interference peak wavelength and the intensity peak wavelength are staggered to a certain extent.
Specifically, an object of the present invention is to provide an organic EL device exhibiting only a slight change in the color purity (CIE chromaticity coordinates) even if the total optical path length of a transparent electrode and an organic layer changes in a prescribed range, and a method of efficiently manufacturing such an organic EL device.
(1) One embodiment of the present invention provides an organic EL device containing an organic layer formed between electrodes at least one of which is a transparent electrode, wherein the total optical path length (t) of the transparent electrode and the organic layer satisfies the following inequality (a) or inequality (b) or both:
Minxe2x88x9220 nm less than t less than Min+20 nmxe2x80x83xe2x80x83(a)
Maxxe2x88x9220 nm less than t less than Max+20 nmxe2x80x83xe2x80x83(b)
wherein t is the total optical path length (nm), Min is the optical path length (nm) at which the CIEx chromaticity or CIEy chromaticity measured according to JIS Z 8701 exhibits a minimum value, and Max is the optical path length (nm) at which the CIEx chromaticity coordinates or CIEy chromaticity coordinates measured according to JIS Z 8701 exhibit a maximum value.
This configuration ensures excellent color purity even if there is a fluctuation (deviation) in thickness of organic layers in a prescribed range, because the use of the optical path length value close to maximum or minimum values exhibits only a small change in the color purity (in the CIE chromaticity coordinates).
With regard to the unit (nm) for the total optical path length (t) of the transparent electrode and the organic layer, and the unit of Min and Max which are the optical path lengths at which the CIEx chromaticity coordinates or CIEy chromaticity coordinates exhibit a maximum or minimum, they are sometimes omitted for the sake of convenience.
(2) In the organic EL device of the present invention, it is preferable that the total optical path length (t) of the transparent electrode and the organic layer be coincided with the optical path length at which the CIEx chromaticity coordinates or CIEy chromaticity coordinates exhibit a minimum value (Min) or the optical path length at which the CIEx chromaticity coordinates or CIEy chromaticity coordinates exhibit a maximum value (Max).
This configuration ensures excellent color purity even if there is the fluctuation in the thickness of organic layers in a prescribed range because the use of the maximum or minimum values as the optical path length value exhibits only a small change in the color purity (in the CIE chromaticity coordinates).
(3) In the organic EL device of the present invention, it is preferable that the intensity peak wavelength (S1) of the organic layer be in the range of about 400 to 490 nm and the total optical path length (t1) of the transparent electrode and the organic layer be coincided with the optical path length at which the CIEy chromaticity coordinates exhibit a minimum value (Min).
This configuration ensures an organic EL device exhibiting excellent pure blue.
This is because a color tone change of blue light is affected by the CIEy chromaticity coordinates rather than the CIEx chromaticity coordinates. The additional reason for causing the total optical path length (t1) to coincide with a minimum value is that the color tone change of blue light is smaller when the total optical path length (t1) coincides with a minimum value.
(4) In the organic EL device of the present invention, it is preferable that the intensity peak wavelength (S2) of the organic layer be in the range of about 580 to 700 nm and the total optical path length (t2) of the transparent electrode and the organic layer be coincided with the optical path length at which the CIEx chromaticity coordinates exhibit a maximum value (Max) or at which the CIEy chromaticity coordinates exhibit a minimum value (Min).
This configuration ensures an organic EL device exhibiting excellent pure red.
This is because a color tone change of red light is affected by the CIEx chromaticity coordinates rather than the CIEy chromaticity coordinates. The additional reason for causing the total optical path length (t2) to coincide with a maximum value or minimum value (a peak or valley) is that the color tone change of red light is small when the total optical path length (t1) coincides with either a maximum value or a minimum value.
(5) In the organic EL device of the present invention, it is preferable that the intensity peak wavelength (S3) of the organic layer be in the range of about 500 to 570 nm and the total optical path length (t3) of the transparent electrode and the organic layer be coincided with the optical path length at which the CIEy chromaticity coordinates exhibit a maximum value (Max).
This configuration ensures an organic EL device exhibiting excellent pure green. This is because a color tone change of green light is affected by the CIEy chromaticity coordinates rather than the CIEx chromaticity coordinates. The additional reason for causing the total optical path length (t3) to coincide with a maximum value is that the color tone change of green light is smaller when the total optical path length (t3) coincides with a maximum value.
(6) In the organic EL device of the present invention, it is preferable that the distribution of the total optical path length (t) of the transparent electrode and the organic layer in the plane be within xc2x120 nm.
This configuration mitigates and reduces the change in the color purity (CIE chromaticity coordinates) due to thickness distribution of the transparent electrodes and organic layers.
Here, the distribution in the plane within xc2x120 nm means that the difference between the maximum and the minimum value of the optical path length in the plane measured by using an ellipsometer is 40 nm or less.
(7) In the organic EL device of the present invention, it is preferable that the organic EL device be provided with an optical path length correcting layer for adjusting the value of the total optical path length (t) of the transparent electrode and the organic layer.
This configuration ensures easy adjustment of the total optical path length (t) of the transparent electrode and the organic layer, which may decrease the change in the color purity (in the CIE chromaticity coordinates) even if the organic layer suffers from the thickness deviation (fluctuation) in a prescribed range.
(8) Another embodiment of the present invention is an organic EL device comprising a blue light emitting organic layer having a intensity peak wavelength of about 400 to 490 nm, a green light emitting organic layer having a intensity peak wavelength of about 500 to 570 nm, and a red light emitting organic layer having a intensity peak wavelength of about 580 to 700 nm, formed between electrodes at least one of which is a transparent electrode, wherein the total optical path length (t1) of the transparent electrode and the blue light emitting organic layer satisfies the inequality, Minxe2x88x9220 nm less than t1 less than Min+20 nm, wherein Min is the optical path length (nm) at which the CIEy chromaticity coordinates measured according to JIS Z 8701 exhibits a minimum value; the total optical path length (t3) of the transparent electrode and the green light emitting organic layer satisfies the inequality, Maxxe2x88x9220 nm less than t3 less than Max+20 nm, wherein Max is the optical path length (nm) at which the CIEy chromaticity coordinates measured according to JIS Z 8701 exhibits a maximum value; or the total optical path length (t2) of the transparent electrode and the red light emitting organic layer satisfies the inequality, Maxxe2x88x9220 nm less than t2 less than Max+20 nm, wherein Max is the optical path length (nm) at which the CIEx chromaticity coordinates measured according to JIS Z 8701 exhibit a maximum value.
This configuration minimizes the change in the color purity (in the CIE chromaticity coordinates) for each three primary colors (red, blue, green) even if there is the fluctuation in the thickness of organic layers in a prescribed range.
Therefore, a color display with excellent color tone is ensured even in the case where the area occupied by the organic layer in the organic EL device is enlarged.
(9) Another embodiment of the present invention is an organic EL device comprising a blue light emitting organic layer having a intensity peak wavelength of about 400 to 490 nm, a green light emitting organic layer having a intensity peak wavelength of about 500 to 570 nm, and a red light emitting organic layer having a intensity peak wavelength of about 580 to 700 nm, formed between electrodes at least one of which is a transparent electrode, wherein the total optical path length (t1) of the transparent electrode and the blue light emitting organic layer satisfies the inequality, Minxe2x88x9220 nm less than t1 less than Min+20 nm, wherein Min is the optical path length (nm) at which the CIEy chromaticity coordinates measured according to JIS Z 8701 exhibits a minimum value; the total optical path length (t3) of the transparent electrode and the green light emitting organic layer satisfies the inequality, Maxxe2x88x9220 nm less than t3 less than Max+20 nm, wherein Max is the optical path length (nm) at which the CIEy chromaticity coordinates measured according to JIS Z 8701 exhibits a maximum value; and the total optical path length (t2) of the transparent electrode and the red light emitting organic layer satisfies the inequality, Maxxe2x88x9220 nm less than t2 less than Max+20 nm, wherein Max is the optical path length (nm) at which the CIEx chromaticity coordinates measured according to JIS Z 8701 exhibit a maximum value.
This configuration minimizes the change in the color purity (in the CIE chromaticity coordinates) for any one of three primary colors (red, blue, green) even if there is the fluctuation in the thickness of organic layers in a prescribed range.
Therefore, a color display with excellent color tone is ensured even in the case where the area occupied by the organic layer in the organic EL device is enlarged.
(10) In forming the organic EL device of the present invention, it is preferable to provide a color changing medium on the light emitting side (namely the EL light extracting side).
This configuration ensures a full color display by appropriately combining color changing media such as a color filter or color changing device even if one type of the organic layer is used.
Therefore, the configuration of the organic EL device can be simplified and the production becomes easy, even if the organic EL device is for a full color display.
(11) Still another embodiment of the present invention provides a method of manufacturing an organic EL device containing an organic layer formed between electrodes at least one of which is a transparent electrode,
wherein the method comprising a forming step of the transparent electrode and the organic layer which satisfies the following inequality (a) or inequality (b) or both:
Minxe2x88x9220 nm less than t less than Min+20 nmxe2x80x83xe2x80x83(a)
Maxxe2x88x9220 nm less than t less than Max+20 nmxe2x80x83xe2x80x83(b)
wherein t is the total optical path length (nm), Min is the optical path length (nm) at which the CIEx chromaticity coordinates or CIEy chromaticity coordinates measured according to JIS Z 8701 exhibit a minimum value, and Max is the optical path length (nm) at which the CIEx chromaticity coordinates or CIEy chromaticity coordinates measured according to JIS Z 8701 exhibit a maximum value.
This method ensures efficient manufacture of organic EL devices with a minimal change in the color purity (CIE chromaticity coordinates) even if there is the fluctuation in the thickness of organic layers in a prescribed range.
(12) In the method of manufacturing the organic EL device of the present invention, it is preferable that an organic layer be formed on a previously fabricated transparent electrode and the total optical path length (t) be adjusted.
This method of manufacture enables the use of a prescribed transparent electrode, for example, a commercially available transparent electrode as is, and adjustment of the total optical path length (t) by adjusting the thickness and refractive index of the organic layer.
(13) In the method of manufacturing the organic EL device of the present invention, it is preferable to provide a step of forming an optical path length correcting layer for adjusting the value of the total optical path length (t) of the transparent electrode and the organic layer.
This method of manufacture ensures easy adjustment of the total optical path length of the transparent electrode and the organic layer, enabling efficient production of an organic EL device which suffers a minimal change in the color purity (CIE chromaticity coordinates) even if the thickness fluctuation occurs in the organic layer in a prescribed range.